Multi-metal planographic printing plates



Oct. 25, 1966 SCHAFLER ET AL 3,280,736

MULTI-METAL PLANOGRAPHIG PRINTING PLATES Filed March 12, 1965 FIG! ALKALINE COPPER l5 l4 L5 '3 CHROME L2 L X F3 ACID COPPER 0N 0/ v ALKALINE COPPER /6 /L7\ I, BASE FIGS CHROME ACID COPPER llu NICKEL ARMANDO B\RLA\N SCHAFLER ALLAN KILROE LOMBARDO ATTORNEYS United States Patent 3,280,736 MULTI-METAL PLANOGRAPHIC PRINTING PLATES Armando Birlain Schatler and Allan Kilroe Lombardo, Mexico City, Mexico, assignors to Metalgamica, S.A., Mexico City, Mexico, a corporation of Mexico Filed Mar. 12, 1965, Ser. No. 439,190 Claims priority, application Mexico, June 8, 1964, 77,504, 77,505; Feb. 26, 1965, 81,292 11 Claims. (Cl. 101-1491) This application is a continuation-in-part of applications Serial Nos. 383,907 and 383,939, both filed July 20, 1964, and application Serial No. 408,306, filed November 2, 1964, now abandoned.

This invention relates to the printing art and more particularly to improved printing plates and methods of producing such plates.

Historically, the original lithographic plate comprised a stone having a smooth surface in which the image to be reproduced was recessed to retain the ink to be transferred to a print. As stone is porous, the smooth surface, which was supposed to be free of ink, tended to accept and accumulate ink which would smear the areas that were supposed to be ink free and spoil the print. It was found that this problem could be overcome by thoroughly wetting the smooth stone surface with water which would fill the pores and repel the ink.

With technological development, plates were devised of other materials that lent themselves to production methods and were more readily worked than stone. However, it was assumed that such plates must have the inherent characteristics of stone in function and operation. It was discovered that copper had an afiinity for ink and was capable of retaining ink within the image recesses, but it was not suitably receptive to water and also was subject to rapid oxidation due to application of water to the smooth non-image surfaces. This condition led to the provision of an outer coating of a material resistant to oxidation and highly receptive to water, such as chromium, zinc and alloys thereof, over the copper, such coating being removed from the image producing areas by an acid etching process.

The foregoing development-s resulted in the production of a plate comprising a ferrous metal base supporting a copper layer having an outer chromium protective coating. It was found that the copper layer was most conveniently formed on the ferrous metal base by electrolytic deposition in an alkaline copper bath. However, to simulate the conditions of the original stone plates, the overlying protective coating was deliberately rendered porous, either mechanically or chemically. With the development of the highspeed, rotary press requiring thin flexible plates, base sheet materials of paper, synthetic plastic and the like, have been employed as well as aluminum and sheet steel but the use of an alkaline copper layer and porous protective coating has been continued for the multimetallic printing plates.

It has long been recognized that the alkaline copper layer has a relatively rough surface with many peak-s, ridges, recesses, crevices and the like. Consequently, the protective chrome coating has also been relatively rough as it tends to follow the copper surface. However, if the chrome is electro-deposited thereon, the surface defects are exaggerated due to the fact that there is a greater than average deposition on the high spots and a lesser than average deposition on the low spots to the extent that in the latter instance the copper may even be left exposed. Attempts have been made to avoid the surface roughness of the alkaline copper layer either by mechanically smoothing the surface, which increases the cost of 3,280,736 Patented Oct. 25, 1966 production, or by substituting other metals or alloys which produce smoother surfaces. It has 'been found, however, that no other metal, even copper alloys such as brass or bronze, have the necessary ability of ink retention.

It has now been determined that the roughness of the porous chrome coating is primarily responsible for several causes of inferior printing ability, both with respect to fidelity of reproduction and to the usable life of the plate. When preparing the plate for use, the chrome layer is covered with a light sensitive emulsion, which is exposed through a transparency that is retained in close juxtaposition by suction. As the suction is not sufficiently effective to draw the transparency against all areas of the plate due to the surface roughness, air pockets are formed therebetween which cause refraction of the light rays so that the initial image is slightly diffused or distorted in some areas.

After the emulsion is developed, the image is then etched in the plate by acid that removes the chrome coating to expose the copper layer. Due to the variable thickness and porosity of the chrome layer, the thinner portions are etched more rapidly than the thicker portions and this will cause an unevenness in lines and/ or an undercoating of the chrome which will cause more rapid wear and breakage of the chrome edges surrounding the dots of the image area so that fidelity and useful life are further reduced.

Finally, in the use of the plate in a rotary press, relatively large quantities of water are required to fill the cavities and/ or pores of the chrome coating so as to repel the ink, and fountain acid must be added to break the surface tension of the water with the chromium. Further, the water is responsible for two basically undesirable results. First, due to the quantity of water necessarily applied to the plate, the water emulsifies with and dilutes the ink which varies the shade or tone value thereof so that larger amounts of ink must be supplied in an effort to maintain uniformity of color and the regulation to control the ink and water balance requires the constant attention of an expert operator.

Secondly, when the plate is used in an offset press the excess amounts of water required for the porous chrome layer causes rapid wetting of the blanket which transfers the ink image from the plate to the paper or other surface being printed. The wetting of the blanket causes dilution and diffusion of the ink image it is intended to transfer, and it also wets the paper to which the image is transferred so that the ink image is further diffused by absorption within the wet paper, the unprinted areas become discolored, and the print must be subjected to a more extensive drying not only to cure the ink but also to dry the paper itself.

The wetting of the blanket and paper print results in a further problem of requiring relatively frequent stopping of the machine to dry and clean the blanket and such stoppages, even for relatively short periods of time require application of a protective coating, such as gum arabic, to the plate to inhibit oxidation through the porous chrome layer. After the blanket is dried and cleaned, the gum arabic or other protective coating must be removed from the plate before printing operations can be resumed. Thus, the loss of production is increased by the time factor involved in applying and removing the protective coating and this time factor, and/ or labor factor is multiplied with respect to a multi-color press by the number of colors involved. Moreover, the protective gum tends to blind the plates under certain conditions.

Having in mind the defects of the prior art equipment, it is the primary object of the present invention to provide a printing plate that will overcome and/ or substantially eliminate all of the aforementioned defects and disadvantages, will produce images with high fidelity, will greatly increase wearabil-ity and useful life, enable and increase of press speed and operation, reduce water and ink consumption, greatly reduce press stoppages, and eliminate the necessity of gumming the plates except for storage.

Another object of the invent-ion is to provide a method of producing printing plates having the foregoing advantages.

A further object of the invention is to provide a printing plate, and a method of producing same, having simplicity, economy and efliciency both of production and in operation.

Another and additional object is to provide a printing plate having ability for being used in lithographic equipment and also in direct printing equipment with a long life and high efiiciency.

The novel features that are considered characteristic of the invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and its method of operation, together with additional objects and advantages thereof, will best be understood from the following description of specific embodiments when read in connection with the accompanying drawing, wherein like reference characters indicate like parts throughout the several figures and in which:

FIG. 1 is an enlarged fragmentary cross-sectional view taken through a partially manufactured plate in accordance with the invention;

FIG. 2 is an enlarged fragmentary cross-sectional view taken through a complete plate in accordance with the invention, and

FIG. 3 is .a cross-sectional view, similar to FIG. 2, of a plate in accordance with a modification of the invention.

Briefly, the present invention resides in the discovery of important features with respect to lithographic printing plates, namely, that, contrary to prior belief, the outer chromium layer must have a smooth, non-porous surface, and that the copper layer underlying the chromium layer 'has greater smoothness and density if electrolytically deposited from an acid copper bath, especially with the addition of a crystal growth or freeing reducing agent or negative catalyst, such as animal glue, aluminum potassium sulfate, or any of the usual brighteners, depending on the bright or matte surface appearance desired.

As the acid copper layer cannot be applied directly to the usual base material, it is necessary to first apply a sublayer such as the usual alkaline copper layer. However, an ancillary feature of the invention resides in providing as the sub-layer a non-porous nickel layer as this increases the overall hardness of the plate and precludes possible migration of moisture .to the underside of the copper.

Referring now more particularly to the invention and with specific reference to the accompanying drawing, a base sheet 10 of any known type is contemplated, such as paper, synthetic plastic such as, for example, an acrylic resin or rigid polyvinyl chloride sheet, or metal, the latter usually being of aluminum or steel. Sheet steel is preferred because it has suflicient flexibility and has greater resistance to wear and deformation. The sheet steel is subjected to a preliminary degreasing treatment but if its surface is not highly finished it is first rubbed or polished to remove or minimize surface imperfections.

The degreasing treatment may be of any known type and, preferably, is effected electrolytically as this also cleans the sheet. The degreased sheet is rapidly spray washed, dip-pickled, and again rap-idly washed. Thereafter, it can be subjected, if necessary, to a neutralizing treatment, and then rinsed, all as well known in the art.

In accordance with the present invention, the ink adhering copper layer comprises an acid copper deposition as will be more particularly described hereafter. However, such acid copper normally cannot be deposited directly upon the usual base sheets, but such sheets must be provided with suitable sub-layers on which the acid copper can be deposited. -In the present instance, as a strong plate is desired, the invention is disclosed as em bodying a steel sheet, treated as previously described, and having a sub-layer 11 which can comprise the usual alkaline copper, or nickel, both of which have a relatively rough uneven outer surface.

It will be apparent to anyone skilled in the art that if a usual porous chromium layer is deposited directly on the alkaline copper or nickel layer, any such chromium layer will have a variable thickness and an uneven outer surface.

In accordance with the present invention, however, the defects of the sub-layer are overcome by depositing thereon an acid copper layer 12 which comprises very fine, densely packed crystals which fill the recesses and cavities of the sublayer 11, FIG. 1, and produce a relatively smooth outer surface, as shown in FIG. 2,

According to one embodiment of the present invention, a steel sheet used as a base having a structure and finish of the highest possible smoothness and on which the defects are corrected such as by a hand polishing operation using a very fine sandpaper, is subjected to a washing operation in order to remove dirt, and as much oil and grease as possible. The degreasing operation is completed by an electrolytic degreasing which comprises dipping the sheet into a solution of a suitable cleanser dissolved in water at a temperature in excess of 134 F. as a cathode, the anode being constituted by the walls of the vessel proper, and passing a current of about 93 amperes per square foot for one minute. The degreased sheet is spray washed with water as fast as possible in order to avoid a further oxidation of the steel. The sheet is dip-pickled in a suitable acid solution such as is conventional in this type of cleansing operation of steel sheets.

The pickled sheet is again spray Washed with water and neutralized by dipping into an alkaline cyanide or caustic alkali solution for about half a minute and then the completely cleansed sheet passes to the alkaline copper plating operation. Sodium cyanide is desirable for neutralization because it is an ingredient of the alkaline copper plating bath.

The alkaline copper plating step is performed in an electrolytic ba-th comprising an aqueous solution of an al-- kali metal cyanide, such as sodium or potassium cyanide, copper cyanide, caustic alkali, and a small amount of Rochelle salt serving as a crystal growth regulator. The composition ranges of the alkaline copper bath which may be advantageously employed in the practice of the invention are:

Composition range, wt.

Ingredient: percent Copper cyanide 36, preferably 4.5. Sodium cyanide (free, uncombined) 1-2.5, preferably 1.5. Sodium hydroxide 13.5, preferably 3. Sodium-potassium tartrate 1.54.5, preferably 3. Water balance.

The alkaline copper plating bath will have a pH of about 8 to 12. The deposition of copper is carried out employing a DC. voltage at a current density of about 10 to about 33, preferably 30, amperes per square foot, a temperature between about 35 and 70 0, preferably about 40 C., and a time of about 2 to 10, preferably about 5, minutes, and using one or more electrolytic copper anodes. The depth of the coating is about 0.1 to 0.25 mils. Preferably the bath is mechanically agitated. The plate acts as cathode.

The alkaline copper coated sheet is passed directly from a neutralizing bath, preferably after rinsing, to an acid copper electrolytic bath which comprises a solution of a suitable copper salt, such as copper sulphate, in a mineral acid such as sulphuric acid, and, if a bright finish is desired, in the presence of a crystal growth reducing agent or negative catalyst, such as glue, agar and other colloidal materials or any of the usual brighteners, either organic or inorganic. The bath is stirred by means of air injected to the bottom of the bath in order to promote its uniformity of composition. If the reducing [agent is of the organic type, the temperature must be maintained under 35 C., inasmuch as a higher temperature will cause the reducing agent to decompose, and impair the performance of this copper plating operation. However, temperatures of from 15 to 45 C. can be used with most of the brighteners.

The acid copper plating bath may contain from about 15% to 25%, preferably 22.5% by weight of copper sulfate, and about .4% to .7%, preferably .6%, by Weight of sulfuric :acid, as well as about .4% to .7%, preferably .6%, by volume of animal glue, agar, crystal growth reducing agents, and commercial organic b-righteners if a bright finish is desired. The plating conditions advantageously include a current density from about 23 to about 33 amperes per square foot, preferably 28 amperes per square foot, for a period of about 5 to minutes, preferably about 8 minutes. The thickness of the acid copper coating will generally range from about 0.1 to about 0.2 mil, or upward to any economical limit.

According to the particular embodiment of the invention, the deposition of the copper from the acid bath produces a fine small crystal, dense layer that fills the recesses of the alkaline copper layer, but the addition to the bath of the crystal growth reducing agent greatly improves this characteristic. The acid copper deposition also produces an inherently relatively smooth, hard, nonporous outer surface having greatly superior ink affinity, and having a bright surface. The density of the acid copper layer greatly improve the strength and wearability not only per se but also of the composite merged alkalineacid copper layer. The density and smoothness of the surface greatly inhibits oxidation and is exceptionally resistant to scratching.

While applicant does not wish to be bound by any theoretical explanation of the reasons why the acid copper deposition serves for smoothing the otherwise uneven surface of the alkaline copper or nickel layer, it has been found that the acid copper layer first builds up a netting of very thin solid bright copper filaments having a very high tensile strength. This netting is thereafter filled in with very small crystals or filaments of copper which are deposited between the above mentioned filarments and which grow to fill the spans therebetween. It has been observed that the filaments form a uniform mat which develops more and more filaments formed of submicroscopic crystals of copper and this mat does not build up after it is formed but rather develops in the manner of filling the structure as time passes. Thus, the filament structure forms a frame to receive the remaining portions of copper deposited, the latter being :eld by the filaments with a very strong bond, thereby precluding this deposit from following the uneven porous surface of the underlayer.

Experiments performed with an equivalent layer of copper deposited from an alkaline bath gave very different results and it has been observed that the deposition is effected with the formation of very weak porous thick filaments which bloom out and tend to grow without order, thereby creating a very uneven rat-her weak layer with characteristics very different from those obtained by the deposition of copper from an acid bath.

The last operation to be effected is to cover the acid copper layer with a chromium layer 13, FIG. 2, which, in accordance with the present invention, is a hard, fine crystal, dense, flexible layer having a smooth non-porous scratchproof surface, with a bright finish, by connecting the plate to the cathode of a vat containing a chromium plating bath. The chromium plating bath comprises an aqueous solution of about 20% to about 35%,

preferably 26%, by weight of chromium trioxide, and an amount of sulfuric acid equal to about 1% of the amount of CrO present. Plating is advantageously performed at a temperature from about 35 C. to about 50 C., preferably 40 C., for a period of about 10 to 20 minutes, preferably about 15 minutes, employing a current density of about to 205, preferably 168 to 187, or specifically about amperes per square foot.

The plate is promptly removed from the bath to avoid acid etching that would impair the surface of the chrome. It has been found that if the temperature is above 50 C. the resistance of the bath increases, requiring greater amperage which results in large, harder and less densely packed crystals producing a relatively brittle layer having a rough porous surface, whereas below 35 C. the resistance of the bath decreases, requiring lesser amperage to avoid scorching the plate and results in a softer layer.

The electrolytic plating operations hercinbefo-re described can be effected on one or both faces of the sheet, depending upon the disposition of the anodes. However, the anodes preferably are arranged to be slightly closer to the central area of the sheet than to the edge portions thereof to effect the deposition of layers of substantially uniform thickness throughout their area. The arrangement of the anodes is particularly important in the chromium plating operation. The anode wall or assembly should be disposed with the central portion thereof about 3 inches closer to the central portion of the cathode than the respective edge portions thereof to obtain a layer of substantially uniform thickness throughout.

When a matte, smooth, very hard, efficient printing plate is desired, the acid copper layer is applied in an electrolytic bath containing the above mentioned amounts of copper salt and mineral acid, but substituting 3 to 5%, preferably 4.5%, of double metal salts, such as aluminum potassium sulfate (potassium alum) or sodium potassium tartrate for the 0.4 to 0.7% crystal growth reducing agent. In this particular embodiment of the invention, the temperature is not critical and temperatures of from 15 C. to nearly the boiling point of the solution can be used. However, it is preferable to operate within the range of from room temperature to 40 C., and still more preferable, at 90 C. for optimum efiiciency. Otherwise, the conditions of operation remain the same as those of the bright plate above described. A very smooth matte appearance of the acid copper layer is obtained, ready to receive the above described hard, non-porous chromium layer.

It has been found, surprisingly, that the period of time used to deposit the chrome layer can be extended in the instant case without cracking thereof when bending the plate to place it on the rolls of the machine, thereby remarkably increasing the thickness of the chromium layer and the hardness thereof. This renders the finished plate useful for direct printing without undue wear for relatively long runs, besides preserving the highly efficient performance thereof on lithographic printing machines. Due to the matte surface of the copper layer the chromium layer also will have a matte surface.

The relatively smooth, hard, non-porous surface of the acid copper layer plus the uniformity of thickness and non-porosity of the chromium layer of both the bright and matte surface plates provides them with a substantially smooth surface having only very minor variations therein. Consequently, the light sensitive coating, when applied thereto will have an equally smooth surface which enables absolute engagement therewith by the transparency throughout their contact area, resulting in highfidelity exposure.

The uniformity of thickness of the chromium layer enables uniformity of treatment with the etching acid so that the image areas 14, FIG. 2, have substantially straight smooth side walls 15 which are perpendicular to the surface of the layer. The non-porosity and evenness of the chromium layer precludes the acid or its fumes from reacting to a greater extent on some portions of the layer than others or from undercutting the chromium around the image areas.

In the use of the plate only very small quantities of water are required to maintain the surface of the chromium in sufficiently moist condition to preclude adherence of ink thereto. Due to the non-porosity and smoothness of the chromium, its surface is devoid of recesses or pits that might tend to trap ink so that the amount of moisture required to wet the surface is so slight that it is hardly discernable to touch and might more appropriately be termed humidity than moisture.

The freedom from ink adherence precludes the necessity of adding fountain acid to the water, and the minor amount of water applied substantially eliminates emulsification and dilution of the ink, thereby increasing color fidelity and reducing the quantity of ink consumed. Moreover, the very minor amount of moisture that is necessary, greatly reduces the wetting of the paper to which the ink is applied, and wetting of the blanket in an offset press. Consequently, the number of press stoppages is greatly reduced.

Due to the greatly superior performance of the plate, the constant services of a highly skilled operator is not necessary. The relatively smooth surfaces of the exposed acid copper image areas are sufficiently protected against oxidation by the greasy ink embedded therein and the non-porosity of the chromium layer avoids the necessity of gumming during stoppages of the press, even over relatively long periods such as week-ends.

The lack of necessity to gum the plates avoids the possibility of blind plates and, of course, results in a saving of material and time. The hardness or strength of the plate due to the compactness and density of the composite copper layers, due to the density of the acid copper deposition, and the hard, dense chromium layer with a strong non-porous surface gives the plate increased strength which enables faster press operation. Consequently, greatly increased production of much higher fidelity is achieved with a considerable saving in cost of operation.

While the basic concept of the present invention, resides in the addition of the bright or matte surface acid copper layer and non-porous chromium layer to any known base and sub-layer, another embodiment of the invention resides in the provision on any type of base sheet, for a mirror bright plate, of a bright nickel sublayer, 110, FIG. 3, instead of the alkaline copper layer. This nickel layer is electrolytically deposited by means of a bath containing suitable nickel salts, such as the chloride or sulfate, together with boric acid, and brighteners of the conventional type. Preferably, the bath will have a total nickel ion content of from 75 to 90 g. per liter, a total chloride ion content of from 13 to 27 g. per liter, and boric acid in amounts which vary between 40 and 50 g. per liter, with a brightener content of from 10 to 20 g. per liter.

As previously described, the nickel plating operation can be effected either on one or both faces, the plate serving as a cathode and the anodes being disposed closer to the center portion to provide uniformity of deposition. A current density of from 9 to 28, preferably 15, amperes per square foot, for approximately to 15, preferably 10 minutes, is preferred, with the temperature of the bath preferably maintained between 57 to 71 C., preferably about 65 C., with a pH of 3.5 to 4.5, preferably 4.0 The bath is agitated by means of air, and continuously filtered by recirculation in order to maintain it absolutely clean. The bright nickel layer is rinsed with water, and the plate may be directly passed to an acid copper bath as previously described.

The addition of the brightener to the nickel reduces crystal growth so that the layer comprises very fine, densely packed crystals resulting in increased strength, which, combined with the dense, fine crystal acid copper layer and nonporous chrominum layer affords a very strong pllate resistant to wear and damage. Moreover, the nickel layer, in contrast to the alkaline copper layer, has a relatively smooth surface so that the acid copper and chromium layers also have very smooth surfaces.

When a matte surface plate is desired, and according to this ancillary feature of the invention, the nickel plating operation is affected in [a electroplating :batlh containing about 20 to 30%, preferably 25% nickel sulfate; about 4 to 5%, preferably 4.5% nickel chloride; and about 3.5 to 4% boric acid, preferably 3.75%, and in the absence of any brighten-er to obtain a matte surface, which will not affect the desired matte appearance of the upper chrome layer. In the deposition operation, it is preferred to use current density of from about 21 to 43, preferably 32 amperes per square foot; a temperature of from room temperature to 56 C., preferably 40 C.; a bath pH of from 5.0 to 6.0 preferably 5.5, and a residense period of time fro-m about 4 to 8 minutes, preferably 5 minutes. Otherwise, the conditions of operation are the same as previously described.

In all of the aforementioned electrolytic treatments, the time period of operation controls the thickness of the deposited layer and that produced in the periods specified affords the maximum combination of flexibility and strength.

The present invention will be more fully understood by the following examples which are to be construed as merely illustrative and non-limitative of the true spirit and scope thereof.

EXAMPLE 1.-ALKALINE COPPER LAYER DEPOSITION A cold roll steel sheet of about 3 x 3 feet, number 20 gauge, was first sanded with sandpaper No. 600 until all the visible oxide and dirt deposits were removed from the surface thereof. The sheet was washed by means of a water spray and Supersol detergent several times to remove as much as possible of the grease and dirt remaining thereon. These operations were performed only on one face of the sheet. The sheet was then immediately dried by means of a dry sponge in order to avoid further oxidation and was held on a tenter-frame by means of screw presses on the four corners which allow exposure of most of the surface on both sides of the sheet.

The sheet mounted on the tenter was immersed in a vat containing an aqueous solution of cleanser of the Udylite Company maintained at a temperature of about 60 C. The metallic wall of the vat was connected to the positive pole of a rectifier transformer and the tenter and sheet unit was connected by means of suitable supporting electrically conducting bars to the negative pole thereof, in order to provide a current of about 93 amperes per square foot. The sheet was left in the cleansing bath for a period of one minute in order to electrolytically remove all grease from both surfaces thereof. The sheet was passed to a water spraying unit and washed to remove the residues of the cleansing or degreasin'g bath.

The degreased sheet was passed to a second vat containing a pickling solution of Aktane 82 (Udylite Company) and was left there completely immersed in the bath for about one and a half minutes in order to complete the de-oxidizing and degreasing operation. The sheet was then again washed by means of a spray washer with abundant water to remove all traces of the pickling acid bath and then was immersed in :a vat containing about 10% of sodium cyanide for a period of /2 minute to completely neutralize the acidity thereof.

The thus prepared steel sheet was then passed to an electolytic vat without any intermediate washing, in order to preserve the sodium cyanide which also forms part of the copper plating bath contained in said vat. The copper plating bath comprised about 4.5% of copper cyanide, about 1.5% of free sodium cyanide and about 3% of caustic soda in water, as well as about 3.5% of sodium potassium tartrate.

The copper plating vat comprised a rectangular metallic receptacle having six electrolytic copper anodes in the form of long narrow strips and vertically arranged in front of one of the side walls of the vat and other four similar anodes on the other side wall of the vat and is provided with a plurality of supporting bus bars, one to support the six anodes, a second one to support the other four anodes and a third one to support and establish contact with the tenter-frame which, in turn, is connected to the sheet. The sheet was immersed in the bath at the center of the gap between both series of anodes and a current of about 30 amperes per square foot was passed through the electrolytic bath by means of a rectifier transformer furnishing a voltage of about two volts. The sheet was left in the bath for about 5 minutes and the bath was constantly stirred mechanically by propellers arranged .at the ends of the vat.

The thus treated sheet was copper plated on both sides with a more uniform dense coating on the side facing the six anodes of the vat, which side was used for further operations, While the deposit on the other side was provided only for purposes of protecting the steel sheet from corrosion and other environmental adverse factors. The denser copper plate was about .2 mil thick.

EXAMPLE 2.DEPOSITION OF NICKEL SUB-LAYER (Bright surface) The first part of Example 1 was followed through the step of washing the steel sheet after the pickling operation. The thus de reased, pickled and washed sheet was directly passed to a nickel plating vat, without an intermediate neutralization step. The nickel plating vat had a form similar to that used for the alkaline copper plating vat of Example 1. Nickel anodes were used.

The sheet was immersed in the vat containing a nickel plating bath comprising 30% nickel sulphate, 6% nickel chloride, 4.125% boric acid, 10 cc. per liter of brightener No. 63 (Udylite Co.) and 5 cc. per liter of brightener No. 61 (Udylite Co.).

A current density of about amperes per square foot was established between the nickel anodes and the sheet, which is connected as the cathode. The sheet was left in the bath for about 10 minutes at a temperature of 65 C., the bath being stirred by means of an air sparger and continuously recirculated through a filter. A bright nickel layer of about .19 :mil was produced. It had a very bright appearance and was very smooth and uniform.

EXAMPLE 3.-DEPOSITION OF NICKEL SUB-LAYER (Matte surface) The first part of Example 1 was followed through the step of washing the steel sheet after the pickling operation. The thus degreased, pickled and washed sheet was directly passed to a nickel plating vat without an intermediate neutralization step. The nickel plating vat had a form similar to that used for the alkaline copper plating vat of Example 1. Nickel anodes were used.

The sheet was immersed in a plating bath comprising nickel sulphate, 4.5% nickel chloride and 3.75% boric acid. A current density of about 32 amperes per square foot was established between the nickel anodes and the sheet which was connected as the cathode. The sheet was left in the bath for about 5 minutes at a temperature of 40 C., the bath having a pH of about 5.5 and being stirred by an air sparger and continuously recirculated through a filter. A matte finish nickel layer of about 0.14 mil was obtained, having a smooth, uniform, opaque surface.

10 EXAMPLE 4.DEPOSITION OF ACID COPPER ON ALKALINE COPPER SUB-LAYER (Bright surface) The alkaline copper plated sheet produced according to Example 1 was polished by means of very fine sand paper (No. 600) and then by means of an abrasive pad in order to give a more uniform smooth surface. The polished copper plated sheet was then washed with water and detergent to remove all traces of the abrasive and dried with a sponge. The sheet was again mounted on the tenter frame and again electrolytically degreased as described in Example 1, washed with water, neutralized by dipping in a bath comprising 5% sulphuric acid for 1.5 minutes and then passed to an acid copper plating unit comprising a rectangular metal vat having 10 vertical strip-like electrolytic copper anodes uniformly distributed in front of the sheet. The tenter frame was hung on a copper bar connected to the negative pole of a rectifier transformer and the anodes were connected to the positive pole thereof.

The vat was filled with an acid copper plating bath comprising 22.5% copper sulphate, 6% sulphuric acid and 6 cc. per liter of a commercial brightener UBAC (Udylite Co.). A current was established by starting the rectifier transformer in order to provide a current density of 28 amperes per square foot. The sheet was allowed to stay for about 10 minutes at a temperature of 30 C. The sheet was removed from the bath and washed with water to remove any residue. A very bright, smooth, small crystal, dense layer of copper having an average thickness of about 0.19 mil. was obtained. The copper plate had a very remarkable smoothness and uniformity, and did not require a polishing operation to correct surface defects, because the deposit itself tended to cover the inherent defects of the alkaline copper layer.

EXAMPLE 5.-DEPOSITION OF ACID COPPER LAYER ON NICKEL SUB-LAYER (Bright surface) The procedural steps of Example 4 were followed using the bright nickel palted sheet produced according to Example 2. A copper plate of about 0.18 mil. was obtained, having an appearance, uniformity and smoothness superior to that produced according to Example 4.

EXAMPLE 6.-DEPOSITION OF ACID COPPER ON ALKALINE COPPER SUB-LAYER (Matte surface) The alkaline copper plated sheetproduced according to Example 1 was polished by means of very fine sandpaper (No. 600) and then by means of an abrasive pad in order to give a more uniform smooth surface. The polished copper plated sheet was then washed with water and detergent to remove all traces of the abrasive and dried with a sponge. The sheet was again mounted on the tenter frame and again electrolytically degreased as described in Example 1, Washed with water, neutralized by dipping in a bath comprising 5% sulphuric acid for 1.5 minutes and then passed to an acid copper plating unit comprising a rectangular metal vat having 10 vertical strip-like electrolytic copper anodes uniformly distributed in front of the sheet. The tenter frame was hung on a copper bar connected to the negative pole of a rectifier transformer and the anodes was connected to the positive pole thereof.

The vat was filled with an acid copper plating bath comprising 22% copper sulfate, 6% sulfuric acid and 4.5% aluminum potassium sulfate. A current density of about 25 amperes per square foot was established and the sheet was allowed to stay in the bath for about 10 minutes at room temperatures. The sheet was removed from the bath and washed with water to remove any residue. A smooth, small crystal dense matte surface layer of copper with an average thickness of .2 mil was obtained.

EXAMPLE 7.DEPOSITION OF ACID COPPER LAYER ON NICKEL SUB-LAYER (Matte surface) The procedural steps of Example 6 were followed using the matte nickel plated sheet of Example 3. A copper plate of about 0.19 mil was obtained.

EXAMPLE 8. CHROMIUM PLATE DEPOSITION ON ACID ALKALINE LAYER (Bright surface) The copper plated sheet produced according to Example 4, after washing with water, was immersed in a chromium plating bath containing 27.5% chromic acid and 0.26% sulphuric acid in water. This bath was poured into a rectangular plating vat having 15 strip-like carbon anodes arranged in front of the working face of the immersed sheet. A current was established to provide a current density of about 185 amperes per square foot and the sheet was allowed to remain for about 15 minutes at a temperature of 40 C. The chromium plated sheet was removed from the vat and washed with water and detergent to remove all traces of the chromium plating bath. The chromium coating was of .05 ml thickness and had a remarkably hard, non-porous, uniform bright surface which could not be scratched by any common metal but hard steel.

EXAMPLE 9.CHRONIUM PLATE DEPOSITION ON ACID COPPER AND NICKEL SUB-LAYER (Bright surface) The nickel plated sheet produced according to Example was treated in accordance with the details of Example 8. A chromium layer was obtained having a thickness of .06 mil, with a still more remarkable hardness and uniformity than the plate obtained according to Example 8.

EXAMPLE 10.CI-IROMIUM PLATE DEPOSITION ON ACID ALKALINE LAYER (Matte surface) The matte copper plated sheet of Example 6 was treated according to the details of Example 8, with the exception that a residence time of about 20 minutes was used. A matte chromium coating having a thickness of about 0.08 mil was obtained, having an extremely, hard, non-porous uniform surface which proved to be highly eificient in direct printing operations.

EXAMPLE 11.CHROMIUM PLATE DEPOSITION ON ACID COPPER-NICKEL LAYER (Matte surface) The matte nickel plated sheet of Example 7 was treated in accordance with the details of Example 10. A matte surface chromium layer having a thickness of 0.07 mil was obtained. This plate proved to be very good for direct printing, long run operations.

Although certain specific embodiments of the invention have been shown and described, it is obvious that many modifications thereof are possible. The invention, therefore, is not to be restricted except insofar as is necessitated by the prior art and by the spirit of the appended claims.

That which is claimed, as new, is:

1. A planographic printing plate comprising a base sheet having bonded to at least one side thereof a nongrained, non-porous hard copper ink adhering layer composed of fine, densely packed crystals, said layer having a hard, inherently smooth, scratch-proof, non-porous surface, and a hard chromium layer bonded to said nongrained copper layer, said chromium layer being a nongrained chromium layer of substantially uniform thickness and composed of fine, densely packed crystals and having a hard, smooth, scratch-proof, non-porous surface, whereby said plate has a significantly longer life and is capable of accurate dot structure that produces high fidelity printing with faithful reproduction and sharp images uniformly throughout prolonged printing runs, without any shadowing in the non-printing areas, at lower ink and water consumption and resulting in less down time of the printing machine.

2. A planographic printing plate according to claim 1, wherein said copper ink adhering layer is bright.

3. A planographic printing plate according to claim 1, wherein said copper ink adhering layer is matte.

4. A planographic printing plate according to claim 3, wherein said chromium layer is matte.

5. A planographic printing plate comprising a base sheet having bonded to at least one side thereof a nongrained, smooth metal sublayer from the group consisting of non-porous nickel and soft copper; a non-grained, nonporous copper ink adhering layer bonded to said metal sublayer composed of fine, densely packaged crystals, said layer having a hard, inherently smooth, non-porous surface; a hard chromium layer bonded to said non-grained copper layer, said chromium layer being a non-grained chromium layer of substantially uniform thickness and composed of fine, densely packed crystals and having a hard, smooth, scratchproof, non-porous surface, whereby said plate has significantly longer life and is capable of accurate dot structure that produce high fidelity printing with faithful reproduction and sharp images uniformly throughout prolonged printing runs, without any shadowing in the non-printing areas, at lower ink and water consumption and resulting in less down time of the printing machine.

6. A planographic printing plate according to claim 5, wherein said metal sublayer is non-grained, smooth, soft copper layer.

7. A platographic printing plate according to claim 6, wherein the respective portions of said copper layer are merged.

8. A planographic printing plate according to claim 6, wherein said base sheet is steel.

9. A planographic printing plate according to claim 5, wherein said'meta'l sublayer is a non-grained, smooth, non-porous nickel layer.

10. A planographic printing plate according to claim 9, wherein said nickel layer is bright.

11. A planographic printing plate according to claim 9, wherein said base sheet is steel.

References Cited by the Examiner UNITED STATES PATENTS 748,004 12/1903 Pancoat 101-1492 758,599 4/1904 Sachers 101-149.2 1,680,097 8/1928 Eaton 101395 2,214,950 9/1940 Aller. 2,250,556 7/1941 Stareck. 2,291,854 8/1942 Whyzmuzis 101-149.2 2,678,909 5/ 1954 Jernstedt et al 204-41 2,800,438 7/ 1957 Stareck et a1 204-41 ROBERT E. PULFREY, Primary Examiner.

DAVID KLEIN, Examiner.

J. A. BELL, Assistant Examiner. 

5. A PLANOGRAPHIC PRINTING PLATE COMPRISING A BASE SHEET HAVING BONDED TO AT LEAST ONE THEREOF A NONGRAINED, SMOOTH METAL SUBLAYER FROM THE GROUP CONSISTING OF NON-POROUS NICKEL AND SOFT COPPER; A NON-GRAINED, NONPOROUS COPPER INK ADHERING LAYER BONDED TO SAID METAL SUBLAYER COMPOSED OF FINE, DENSELY PACKAGE CRYSTALS, SAID LAYER HAVING A HARD, INHERENTLY SMOOTH, NON-POROUS SURFACE; A HARD CHROMIUM LAYER BONDED TO SAID NON-GRAINED COPPER LAYER, SAID CHROMIUM LAYER BEING A NON-GRAINED CHROMIUM LAYER OF SUBSTANTIALLY UNIFORM THICKNESS AND COMPOSED OF FINE, DENSELY PACKED CRYSTALS AND HAVING A HARD, SMOOTH, SCRATCHPROOF, NON-POROUS SURFACE, WHEREBY SAID PLATE HAS SIGNIFICANTLY LONGER LIFE AND IS CAPABLE OF ACCURATE DOT STRUCTURE THAT PRODUCE HIGH FIDELITY PRINTING WITH FAITHFUL REPRODUCTION AND SHARP IMAGES UNIFORMLY THROUGHOUT PROLONGED PRINTING RUNS, WITHOUT ANY SHADOWING IN THE NON-PRINTING AREAS, AT LOWER INK AND WATER CONSUMPTION AND RESULTING IN LESS DOWN TIME OF THE PRINTING MACHINE. 